package com.packt.learnjava.ch14_streams;
import java.util.List;
import java.util.stream.DoubleStream;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
public class NumericStreams {
public static void main(String... args){
range();
boxed();
mapToObj();
mapTo();
flatMapTo();
sumAndAverage();
}
private static void range(){
IntStream.range(1, 3).forEach(System.out::print); //prints: 12
System.out.println();
LongStream.range(1, 3).forEach(System.out::print); //prints: 12
System.out.println();
IntStream.rangeClosed(1, 3).forEach(System.out::print); //prints: 123
System.out.println();
LongStream.rangeClosed(1, 3).forEach(System.out::print); //prints: 123
}
private static void boxed(){
//IntStream.range(1, 3).map(Integer::shortValue) //compile error
// .forEach(System.out::print);
IntStream.range(1, 3).boxed().map(Integer::shortValue)
.forEach(System.out::print); //prints: 12
System.out.println();
//LongStream.range(1, 3).map(Long::shortValue) //compile error
// .forEach(System.out::print);
LongStream.range(1, 3).boxed().map(Long::shortValue)
.forEach(System.out::print); //prints: 12
System.out.println();
//DoubleStream.of(1).map(Double::shortValue) //compile error
// .forEach(System.out::print);
DoubleStream.of(1).boxed().map(Double::shortValue)
.forEach(System.out::print); //prints: 1
}
private static void mapToObj(){
IntStream.range(1, 3).mapToObj(Integer::valueOf)
.map(Integer::shortValue)
.forEach(System.out::print); //prints: 12
System.out.println();
IntStream.range(42, 43).mapToObj(i -> new Person(i, "John"))
.forEach(System.out::print); //prints: Person{name='John', age=42}
System.out.println();
LongStream.range(1, 3).mapToObj(Long::valueOf)
.map(Long::shortValue)
.forEach(System.out::print); //prints: 12
System.out.println();
DoubleStream.of(1).mapToObj(Double::valueOf)
.map(Double::shortValue)
.forEach(System.out::print); //prints: 1
}
private static void mapTo() {
List<String> list = List.of("one", "two", "three");
System.out.println();
list.stream().mapToInt(String::length).forEach(System.out::print); //prints: 335
System.out.println();
list.stream().mapToLong(String::length).forEach(System.out::print); //prints: 335
System.out.println();
list.stream().mapToDouble(String::length).forEach(d -> System.out.print(d + " ")); //prints: 3.0 3.0 5.0
System.out.println();
list.stream().map(String::length).map(Integer::shortValue).forEach(System.out::print); //prints: 335
System.out.println();
//list.stream().mapToInt(String::length)
// .map(Integer::shortValue) //compile error
// .forEach(System.out::print);
list.stream().map(String::length)
.map(Integer::shortValue)
.forEach(System.out::print); //prints: 335
}
private static void flatMapTo() {
List<Integer> list = List.of(1, 2, 3);
System.out.println();
list.stream().flatMapToInt(i->IntStream.rangeClosed(1, i)).forEach(System.out::print); //prints: 112123
System.out.println();
list.stream().flatMapToLong(i->LongStream.rangeClosed(1, i)).forEach(System.out::print); //prints: 112123
System.out.println();
list.stream().flatMapToDouble(DoubleStream::of).forEach(d -> System.out.print(d + " ")); //prints: 1.0 2.0 3.0
System.out.println();
List.of("one", "two", "three").stream()
.flatMapToInt(s->IntStream.rangeClosed(1, s.length()))
.forEach(System.out::print); //prints: 12312312345
}
private static void sumAndAverage() {
int sum = IntStream.empty().sum();
System.out.println(sum); //prints: 0
sum = IntStream.range(1, 3).sum();
System.out.println(sum); //prints: 3
double av = IntStream.empty().average().orElse(0);
System.out.println(av); //prints: 0.0
av = IntStream.range(1, 3).average().orElse(0);
System.out.println(av); //prints: 1.5
long suml = LongStream.range(1, 3).sum();
System.out.println(suml); //prints: 3
double avl = LongStream.range(1, 3).average().orElse(0);
System.out.println(avl); //prints: 1.5
double sumd = DoubleStream.of(1, 2).sum();
System.out.println(sumd); //prints: 3.0
double avd = DoubleStream.of(1, 2).average().orElse(0);
System.out.println(avd); //prints: 1.5
}
}
